The invention relates generally to robots for handling semiconductor substrates during fabrication, and more particularly to end-effectors for transferring substrates into and out of high temperature process chambers.
Some semiconductor processes are conducted at elevated wafer temperatures to achieve a desired process result. Semiconductor substrates or wafers are heated up inside the process chamber such as by direct physical contact with a heated wafer chuck or by radiation from radiant heating sources. As the process completes, it is advantageous to cool the processed wafers before placing them back in a wafer cassette. Without cooling, hot wafers may damage cassettes, such that more expensive hightemperature cassettes would be required to hold hot wafers. Additionally, the cassettes may not be safe for workers to handle.
Traditionally, hot wafers are cooled with a stand-alone wafer cooling station. A robot picks a hot wafer from the process chamber and places it on the wafer cooling station, where the wafer is allowed to cool down before being placed in the cassette. Water circulates through channels or tubes inside the cooling station to remove heat drawn from the wafer, thereby keeping the station cool enough to continue drawing heat from subsequent wafers.
Using a stand-alone wafer cooling station to cool hot wafers requires an additional wafer pick-and-place motion and a waiting period for the wafer-to-station heat transfer to complete, representing process overhead. This overhead may not lower the equipment throughput if the time required to complete a particular process is long enough and the robot is fast enough that the robot is always waiting for the process chamber to be ready for the next wafer. However, this overhead can cause a significant throughput reduction if the process is short enough that the process chamber is waiting for the robot to complete wafer transfer.
In the semiconductor industry, photoresist ashing or stripping is one of the short processes in which this type of wafer handling overhead can dramatically lower the overall throughput of the resist stripping reactor. Moreover, as process technology improves and processing speeds increase, cooling time can become a limiting factor for wafer throughput in other integrated circuit fabrication steps.
Accordingly, there is a need to minimize the wafer cooling overhead resulting from integrated circuit fabrication steps.
In satisfaction of this need, robot end-effectors are disclosed for minimizing cooling overhead of processed wafers between stations is disclosed. Means for transporting a wafer between processing stations is provided with heat transferring mechanisms.
In accordance with one aspect of the invention, an end-effector is provided for transporting substrates within a semiconductor fabrication environment. The end-effector includes a paddle portion that is configured to underlie at least 60% of a substrate to be processed, and thereby support and conductively exchange heat with the substrate. A handle portion is integrally formed with the paddle portion and is configured to connect the paddle portion to a robot arm. The end-effector also includes an integrated cooling mechanism configured to dissipate heat from the end-effector by convection.
The cooling mechanism of one embodiment includes a plurality of fins extending from the handle portion and providing a high surface area for heat dissipation. As the end-effector moves, air flows through the fins to force convection without introducing more particles into the processing environment. In another embodiment, cooling fluid channels are provided in the end-effector to carry heat by convection from the paddle region to the handle portion and/or from the handle portion outside the end-effector. The channels can be closed heat pipes house phase transition fluid or open loop channels for circulating coolant fluid.
In accordance with another aspect of the invention, a method is provided for cooling and transferring processed substrates with a dual arm robot. The method includes picking up a first hot substrate with a first end-effector and transferring heat from the first hot substrate to the first end-effector. The first hot substrate is moved to storage cassette with the first end-effector. A second hot substrate is picked up with a second end-effector and heat is transferred from the second hot substrate to the second end-effector. The first end-effector is cooled in the interim. The second hot substrate is moved to a second storage cassette with the second end-effector.
In the preferred embodiment, cooling is conducted by picking up a first cold substrate from a cassette with the first end-effector after dropping the first hot substrate and carrying it to a process chamber. Preferably, each of the two end-effectors alternately pick up hot substrates, such that while one end-effector carries a hot substrate, the other end-effector is allowed to cool, particularly by transferring heat to a cold substrate. Most preferably, the end-effectors include one or more cooling mechanisms as described with respect to the first aspect described above.
In accordance with another aspect of the invention, a method is provided for handling substrates between a storage area and a high temperature processing chamber. The method includes removing a processed substrate from a high temperature processing chamber with a substrate handler. The substrate handler includes a paddle portion in thermal contact with a handle portion, and the handle portion connects the paddle portion to a robot arm. Heat transfers conductively from the substrate to the paddle portion. This heat is, in turn, transferred from the paddle portion to the handle portion. Heat is then actively dissipating heat from the handle portion by forced convection.